1. Field of the Invention
This invention relates to static charge neutralizers, which are designed to remove or minimize static charge accumulation. Static charge neutralizers remove static charge by generating air ions and delivering those ions to a charged target.
One specific category of static charge neutralizer is the ionizing blower. An ionizing blower normally generates air ions with a corona electrode, and uses a fan (or fans) to direct air ions toward the target of interest.
Monitoring or controlling the performance of a blower utilizes two measurements.
The first measurement is balance. Ideal balance occurs when the number of positive air ions equals the number of negative air ions. On a charge plate monitor, the ideal reading is zero. In practice, the static neutralizer is controlled within a small range around zero. For example, a static neutralizer's balance might be specified as 0±2 volts.
The second measurement is air ion current. Higher air ion currents are useful because static charges can be discharged in a shorter time period. Higher air ion currents correlate with low discharge times that are measured with a charge plate monitor.
In practice, charge plate monitors are not used for continuous monitoring or feedback control. The expense would be prohibitive.
This instant invention describes a practical method and apparatus for monitoring and controlling ionizing blowers.
2. Description of Related Art
There are many sensors suggested to monitor and control ionizing blowers. The two most common sensors are: (1) a conductive grid connected to a low current amplifier, and (2) a three electrode combination.
The conductive grid sensor measures air ion current, and uses this information to assess ion balance. The conductive grid works, but it possesses disadvantages.
One disadvantage of the conductive grid sensor is that the conductive grid consumes a large fraction (as much as 30%) of the blower's air ion output. Hence, the blower operates at a low efficiency.
A second disadvantage of the conductive grid sensor is its response to environmental interference. The grid sensor is exposed to external electric fields, which induce unwanted currents that contribute noise to the measurement. Fans, heaters, lights, and motors are examples of devices which generate electric fields. In the presence of environmental interference, both accuracy and sensitivity are compromised.
Any attempt to shield the grid sensor from external electric fields creates an obstacle to air flow. It also makes the blower larger. Moving the grid away from electric field generators limits installation options.
A third disadvantage of the conductive grid sensor is that it can only measure net current. And net current contains no information concerning total ion output. For example, 110 nanoamps of positive air ion flow and 100 nanoamps of negative air ion flow would read 10 nanoamps of positive air ion flow. And 15 nanoamps of positive air ion flow and 5 nanoamps of negative air ion flow would also read 10 nanoamps of positive air ion flow.
A three electrode sensor can measure balance and air ion current. This sensor comprises of two reference electrodes and one voltage or current sensitive electrode. However, it has the same disadvantages as the grid sensor, such as high sensitivity to electrical noise.
A new type of sensor is needed for monitoring and controlling ionizing blowers. The new sensor should measure balance and air ion current. And it should be insensitive to environmental interference.